/*
 * Copyright (c) 2011-2012 Alexander Dubu
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *
 * o  Redistributions of source code must retain the above copyright notice,
 *    this list of conditions and the following disclaimer.
 *
 * o  Redistributions in binary form must reproduce the above copyright notice,
 *    this list of conditions and the following disclaimer in the documentation
 *    and/or other materials provided with the distribution.
 *
 * o  Neither the name Axil nor the names of its contributors may be used to
 *    endorse or promote products derived from this software without specific
 *    prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 */
package axil.etc;

import axil.api.AxilObject;
import axil.api.extend.Environment;
import axil.api.extend.Parameters;
import axil.api.extend.Source;
import axil.engine.function.Functor;
import axil.stdlib.numbers.type.Int;
import axil.vm.stack.StackFrame;

import java.util.Comparator;

import static axil.framework.Functions.*;


/**
 * A Java comparator, but one that uses an Axil function as the basis for
 * comparison.
 */
public class CompareFunctor implements Comparator<AxilObject> {
	private Environment env;
	private Parameters params;
	private Source source;
	private Functor func;


	public CompareFunctor(Environment env, Parameters params, Source source,
	                      Functor func) {
		this.env = env;
		this.params = params;
		this.source = source;
		this.func = func;
	}


	/**
	 * Compares its two arguments for order.  Returns a negative integer,
	 * zero, or a positive integer as the first argument is less than, equal
	 * to, or greater than the second.
	 */
	public int compare(AxilObject a, AxilObject b) {
		StackFrame sf = StackFrame.create(params, source, func.ids());
		sf.a(a);
		sf.b(b);
		AxilObject r = func.call(env, sf);
		if (r instanceof Int) {
			return ((Int)r).value();
		}
		throw error(axil(), "bad-comparator",
		            nv("value", r), nv("type", r.type()));
	}
}
